1. Field of the Invention
This invention relates to an article of manufacture and an apparatus for feeding sheets from stacks of sheets and, in particular, to separating an article and apparatus for separating the top sheet from the rest of the sheets in order to feed one sheet at a time.
2. Prior Art
In most printing, duplicating and copying machines there is an apparatus for feeding copy sheets from a stored, stack of sheets into the machine for further processing. In order to properly perform its functions, a sheet feeder should feed only one sheet at a time. A recurrent problem with such sheet feeders in the feeding of two or more sheets at a time, either together or overlapping one another. Such multifeeding of sheets can be minimized by using a vacuum sheet feeder apparatus which uses a vacuum means to separate the top sheet from a stack of sheets. A belt conveyor or other suitable means is used to carry the top, separated sheet away from the stack. Although such vacuum feeders are highly reliable, they are also expensive, bulky, noisey, and thus ill-suited for a copying machine that is to be used in an office environment.
A simpler, smaller, and less expensive apparatus is a friction sheet feeder in which a suitable sheet advancing means, such as an intermittently driven feed roller, frictionally engages the top sheet to feed it from the stack. The top sheet is separated by any suitable separator means, such as a pair of corner separators disposed at opposed corners of the stack. In operation, the leading edge of the top sheet is slightly deformed or buckled against the corner separator under the influence of the friction feed rollers. Since the frictional feeding force is always set to be greater than the sheet-to-sheet drag, the top sheet ultimately is separated and advanced from the stack. However, a common and repeated problem is that one or more sheets are carried along with the top sheet.
Such a problem is commonly referred to as a multifeed and can occur at any time. It is believed to be caused by inter-sheet frictional forces that are influenced by such ambient factors as temperature, humidity, the normal force of the feed roller, as well as by inherent factors, such as the sheet finish, the type and grade of sheet, and the mechanical properties of the sheet, e.g. beam strength. Some have tried to solve the problem of multifeeds by controlling the environment of sheet feeder to minimize the effects of the ambient factors. Accordingly, sheet feeders have been equipped with temperature, humidity and other environmental controls. Others have designed special sheet feeders which can properly handle only a specific type or types of sheets. It is also believed that multifeeding may be caused, at least in part, by minute mechanical interlocking or hooking of the frayed edges of a stack of sheets. Such fraying can result from the manufacture of the paper when dull knives are used to cut the paper into standard size sheets. To remedy that problem it has been proposed to prop up the center of a stack of sheets, disposing the stack convexly, with respect to the friction feeder, in order to separate or fan out the edges of the stack. Still others have devised various sheet separators which are said to improve the performance of the feeders. See for example, U.S. Pat. Nos. 3,601,389 and 3,574,348. In spite of such attempts, the problem of multifeeds persists and there remains a long felt, unsatisfied need for a reliable friction sheet feeder.
It is an object of this invention to provide a reliable sheet feeder.
It is also an object to provide a sheet feeder that minimizes the occurrence of multifeeds. A further object is to provide a two stage sheet separator using a first stage pair of corner separators and a second stage pair of retarding blades to inhibit the advance of all but the top sheet.
An object is to provide a retarding blade transverse to a predetermined path of the leading edge of the top sheet and having a groove for receiving the leading edges of sheets advanced along said predetermined path.
A further object is to provide an apparatus for optimizing the beam strength of a stack of sheets in order to assist the separation of the top sheet therefrom.
It is also an object to provide a means for concavely disposing a stack of sheets with respect to a friction sheet feeding means.
An added object is to provide a pair of triangular wedges one in each opposed corner along the bottom of the leading edge of a stack of sheets in order to concavely dispose the stack of sheets and thereby increase the beam strength thereof.
The foregoing as well as other objects and advantages will be understood from the following summary and detailed description, the accompanying drawings and the appended claims.